Visual attention deficits in Alzheimer's disease: an fMRI study.

Cognitive and neuroscience studies indicate that attentional operations are impaired in Alzheimer's disease (AD). Our goal was to define the anatomical areas of activation associated with visual attention processing and to define deficits or changes that may occur in AD patients compared with control group. Thirteen AD patients and 13 age- and education-matched normal controls were tested in two visual search tasks (one was a conjunction task, where feature binding is required. The other was a subset task, where group stimuli is needed without feature binding) using fMRI techniques. After stereotactical normalization, voxel-by-voxel t statistics was used to compare activated brain areas between patients and control subjects. Our findings suggest that both search tasks are controlled by partially overlapping cerebral networks, including parietal, frontal and occipital-temporal cortical regions and primary visual cortex. The AD patient group showed less activation in both parietal lobes and the left frontal regions, while increased activation was found in the right frontal lobes and the right occipito-temporal cortical regions with the conjunction task. In the subset task, decreased activation in AD patients was seen in the left parietal lobe and bilateral frontal lobes, while increased activation was seen in both medial temporal lobes. In addition, for the comparison between tasks, The difference is very small for AD patients. Control group showed a higher amplitude in the right prefrontal region, temporal cortical regions and parietal lobe. These results indicate that attention deficits in AD patients may be attributed to both binding problem and grouping inefficiency.